Dirk Bruere at NeoPax wrote:
On 15/03/2010 22:17, Ian Bell wrote:
Dirk Bruere at NeoPax wrote:
On 15/03/2010 10:03, Ian Bell wrote:
Mr.T wrote:
"Arny Krueger" wrote in message
...
Arny I'm really surprised I have to spell it out for you,
a passive analog attenuator reduces both signal AND noise
at *it's output* (amplifier input)
Of course, but read what I wrote: it does nothing to reduce the
noise at
the
output of the amplifier which is often the weakest link.
Read what I wrote, I never said it did. But the OP thinks his
amplifier is
not the problem.
The OP *wasn't*
complaining about his amplifiers noise!
In this case he had an amplifier with atypically low noise.
So why bring up something irelevant to the actual discussion then?
IF that was his problem, asking for a low noise sound
card is even more stupid!
The problem of coming up with an audio interface with dynamic range
and
SNR
108 dB was solved long ago.
Never in dispute.
****, it's a pretty woeful amplifier that only gets 80dB
S/N these days! Hardly "audiophile" quality!!!!
Look at the spec sheets for some modern integrated amps.
Yep, "audiophile" grade pretty much around 100dB these days.
Your definition of "audiophile" grade may differ of course.
I'm here to tell you that many power amps that spec 100 dB are a
little
optimistic.
Sure, and many that aren't, and I've measured quite a few.
For a tube amp perhaps, but power amps with over 100dB
S/N are easily obtained these days.
They can be obtained, but 100 dB is not a low mark, especially if you
test
them on the bench.
Also consider that most CD players are attached to integrated amps,
not
power amps.
Irrelevant to the current discussion. You are free to make a
completely
separate point of course, but don't drag me into it.
Like I said, the OPs specific problem is in my views resolved days
ago.
Years ago in fact, but he doesn't seem to realise it.
MrT.
And both of you please stop using s/n when you mean dynamic range -
they
are not the same thing not to mention simply quoting a totally
unqualified dB figure is quite meaningless.
s/n as in max voltage output with an input of 0dB to the voltage
output with no input signal.
LOL, that's is awful.
0dB has no meaning.
http://jtauber.com/decibels/
"There are actually two reference voltages in use. 1V and 0.775V. When
using the former as the reference, we write 'dBV' and when using the
latter we use 'dBu'. "
Either would do.
Indeed, and most professional equipment operates at +4dBu and some at
+8dBu and then again a lot of commercial power amps have an input
sensitivity of 2V for full output.
Any of these would do, the point is we are not told which.
Input termination in both cases is unspecified
As per manufacturers guidelines
I very much doubt the manufacturer says how the input is terminated when
he measures the amp output noise but I very strongly suspect he short
circuits it to give him the lowest noise figure. Of course you will not
achieve this figure when connected to a real source.
Output termination is unspecified.
As per manufacturers guidelines
Which are what?
No bandwidth is specified.
We are talking "audio" so perhaps we can suggest it just might be
somewhere between 20Hz and 20,000Hz?
Yes, but when measuring noise it is very important. Often a 15KHz
bandwidth with well defined slopes is used because it gives a total
equivalent noise bandwidth of 20KHz which is not the same as a flat
response from 20Hz to 20KHz but is does give a better figure.
No weighting or not is specified.
True.
No mention of whether the measurements are rms, peak, quasi-peak
etc
Well, maximum Music Power obviously! [not]
LOL
Cheers
Ian
Variations in the way the above are specified can make a large
difference to the 'measured' value and I bet you can guess which set the
marketing department will want to choose.